The invention relates to a data carrier which is adapted to provide contactless communication with a communication station and which has a substrate means and which has a communication resonant circuit connected to the substrate means and consisting of at least one communication coil and of a capacitor configuration which is connected to the at least one communication coil in an electrically conductive manner, which communication resonant circuit has a resonant frequency which should have a nominal value, and which has changing means for changing the resonant frequency of the communication resonant circuit, which changing means are adapted to change the resonant frequency from an initial value to higher frequency values.
Such a data carrier of the type defined in the opening paragraph is commercially available, as is known to the applicant, and is consequently known. In the known data carrier the substrate means is formed by a plastic foil and the capacitor configuration includes a changing means in the form of a tuning capacitor which is formed with the aid of a comb-shaped electrode and a strip-shaped electrode, the strip-shaped electrode being disposed perpendicularly to the comb teeth of the comb-shaped electrode and the tuning capacitor having at least one cut-out which extends through at least one comb tooth of the comb-shaped electrode and the strip-shaped electrode as well as the plastic foil. Owing to the provision of a cut-out in the known data carrier the value of the tuning capacitor can only be reduced and, consequently, the value of the resonant frequency of the communication resonant circuit can only be increased. This is the reason why in the series production of the known data carrier the resonant frequency of all the data carriers produced is initially made too low as compared with the desired nominal value, which is achieved by forming tuning capacitors whose value is too large in relation to a nominal value, a reduction of the value of the tuning capacitor and, consequently, an increase of the value of the resonant frequency of the communication resonant circuit being achieved by a trimming operation after production, in the present case by a punching operation. As a result of this, all the known data carriers thus produced, without exception, should be subjected to such a trimming operation, i.e. to a punching operation, which involves a substantial expense and leads to a considerable increase in production cost.
It is an object of the invention to preclude the aforementioned problems and to provide a data carrier which can be manufactured advantageously at substantially lower cost in the case mass production.
According to the invention, in order to achieve the aforementioned object with a data carrier of the type defined in the opening paragraph, the changing means are, in addition, adapted to change the resonant frequency from the initial value to lower frequency values.
With a data carrier in accordance with the invention it is achieved in a simple manner that a change of the value of the resonant frequency of the communication resonant circuit is possible not only in the sense of an increase but also in the sense of a decrease. This has the advantage that during the mass production of a data carrier in accordance with the invention the resonant frequency values need not be kept low intentionally in order to enable it to be subsequently increased during a trimming operation in order to trim a tuning capacitor, but that during mass production it is attempted to obtain a resonant frequency whose value is within given tolerance limits for as many as possible data carriers in accordance with the invention thus manufactured, without an additional adjustment operation being required. An advantageous consequence of this is that during the mass production of a data carrier in accordance with the invention no adjustment operation of any kind, i.e. no alignment operation, for example a trimming operation, is required for all those data carriers whose resonant frequency values lie within given tolerance limits and essentially correspond to a predetermined nominal value, which in practice is actually so for approximately 90% of the manufactured data carriers, as a result of which an adjustment or trimming operation is required for only a comparatively small number of data carriers, which is advantageous both in view of a minimal production time and in view of minimal production cost.
It has proved to be very advantageous when a data carrier in accordance with the invention in addition has the characteristic features as defined in claim 2. This results in a very simple construction.
It has proved to be particularly advantageous when a data carrier as described in the preceding paragraph in addition has the characteristic features as defined in claim 3 and claim 4. These constructions have proved to be particularly advantageous in numerous tests carried out in the course of the development of a data carrier in accordance with the invention.
The above-mentioned as well as further aspects of the invention will become apparent from the embodiment described hereinafter by way of example and will be elucidated with reference to this example.